You can usually waive that plan if you show coverage that meets your school's criteria, such as minimum annual benefits, a maximum deductible, and a US-based claims office.
On a J-1 visa? US Department of State rules also require at least $100,000 in medical benefits per accident or illness, $25,000 for repatriation of remains, $50,000 for medical evacuation, and a deductible of no more than $500 per accident or illness. This applies to your J-2 dependents too.
Waiver deadlines are strict. Missing yours usually means you're charged for the school plan for the whole term.